Underground storage tanks are widespread, primarily at gasoline service stations. The service station tanks are large capacity tanks typically holding 10,000 to 20,000 gallons of gasoline. They are buried sufficiently deep that their top surface is about one to four feet below ground surface. The storage tank and its accessories still are regularly exposed to water, as from rain water ground seepage or a high water table.
A containment sump is mounted on top of the underground storage tank either directly or indirectly. The sump houses piping, pumps, and other accessories needed for proper tank use. The typical containment sump is about one to three feet in diameter and about one to three feet in height. It further has a lid. The lid is accessed by a manhole located in the ground above the sump. A manhole cover at the surface is removable to gain access to the sump's lid and ultimately the sump's interior if needed.
A problem experienced by many existing containment sumps is that water flows into the sump's interior—even to the extent of filling it on occasion. The water can enter the sump by flowing around an edge of the manhole cover and down onto the sump's lid. Gaskets and other seals designed to prevent this are successful to a limited degree. Even with a properly sealed manhole cover and sump lid, water still seeps in. The water further can enter into the sump through openings provided in the sump's wall to accommodate piping as well as through wall gaps, cracks, or holes which can form over time.
Water seepage into containment sumps is a recognized problem in the industry. Service station operators are aware of the problem and most have tried to address it. The problem is compounded by the fact water build-up in the containment sump likely is not immediately recognized. The manhole cover and the sump's lid must first be removed. This requires time and usually simply is not done even though environmental laws may require it. It is, of course, checked when any water seepage problem manifests itself, e.g. by an electric malfunction or contaminated gasoline. By then, the damage is done.
The fact remains there is an obvious need for preventing water from entering containment sumps of underground storage tanks. The need is felt with existing storage tank sumps and with new tank installations. There has now been developed an effective method of preventing water from entering the containment sumps. The method is useful in a retrofit setting as well as in a new installation setting. The method further includes a means for periodically checking for water seepage in a safe convenient manner.